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ADDING NEW CONTINUOUS QUERIES TO A DATA STREAM MANAGEMENT SYSTEM OPERATING
ON EXISTING QUERIES

Abstract

A new continuous query to a data stream management system (DSMS) may use a
stream or a relation which may or may not be used by continuous queries
previously registered in the DSMS. The DSMS is programmed to modify an
execution plan to accommodate execution of the new query while continuing
to execute the previously registered continuous queries. The modified
execution plan may include new operators and/or share existing operators.
The DSMS is programmed to cause operators which output a relation to
propagate a current state of the relation to each newly-coupled operator
that uses the relation. The current state is propagated only to operators
that have been newly coupled and have thus not yet received any state
information previously. After propagation of current state to
newly-coupled operators, results of processing any new data for the
relation are supplied to all operators coupled thereto, including
newly-coupled operators and existing operators.

1. A computer-implemented method of managing a plurality of streams of
data in a computer, the method comprising:processing the plurality of
streams, to execute thereon a plurality of continuous queries based on a
global plan;during said processing, receiving a new continuous query to
be executed;during said processing, identifying from the global plan, a
first operator that supplies data on the relation;during said processing,
modifying the global plan by coupling the first operator to a second
operator to be used to implement the new continuous query, thereby to
obtain a modified plan;prior to execution of the new continuous query,
propagating from the first operator to the second operator, a current
state of a relation if said relation is output by the first
operator;altering said processing, to cause execution of the new
continuous query in addition to said plurality of continuous queries,
based on the modified plan; andoutputting from said computer, a stream
generated based at least partially on processing of said data by
executing the new continuous query.

2. The method of claim 1 wherein:said propagating from the first operator
to the second operator is performed at a time when the first operator is
awakened subsequent to creation of the modified plan.

3. The method of claim 1 wherein:each said propagating is performed in an
idempotent manner relative to at least one predetermined soft exception.

4. The method of claim 1 further comprising:initializing at least one
parameter of a queue during said modifying; andchanging at least said
parameter of said queue during each said propagating;wherein said queue
supports multiple readers and is coupled between the first operator and
each operator in a group of operators in the global plan.

5. The method of claim 1 wherein:the relation is represented incrementally
in the global plan, as a plurality of tuples with each tuple being time
stamped; andall tuples of the relation having a time stamp older than a
current time represent said current state.

6. A computer-readable storage medium encoded with instructions for a
computer to process streams of data using a plurality of continuous
queries in a data stream management system, the instructions
comprising:instructions to execute a global plan for execution of the
plurality of continuous queries;instructions to receive a new continuous
query to be executed;instructions to check if new continuous query
comprises a relation already referenced in a continuous query among the
plurality of continuous queries being executed as per the global
plan;instructions to instantiate a first operator corresponding to said
relation if a result of said checking is false;instructions to mark, as
being available for implementation of said new continuous query, a second
operator currently present in the computer and corresponding to said
relation, if the result of said checking is true;instructions to
instantiate a third operator corresponding to said new continuous
query;instructions to couple to the third operator, an appropriate
operator selected to be one of the first operator and the second
operator, wherein selection of the appropriate operator is based on the
result of executing said instructions to check;instructions to propagate
to at least the third operator, a current state of the relation, in
response to start of execution thereof, wherein said propagating is
performed in a transparent manner relative to soft
exceptions;instructions to supply to all operators coupled to the
appropriate operator, information related to a new state of the relation,
wherein said all operators comprise at least said third operator;
andinstructions to output from said computer, a stream generated based at
least partially on processing of said data by executing each of said
operators.

7. The method of claim 6 wherein:said all operators comprise at least a
fourth operator already present in the global plan.

8. The method of claim 6 wherein:said propagating of current state is
performed at a time when the appropriate operator is next awakened.

9. The method of claim 6 wherein:said propagating of current state is
performed in an idempotent manner relative to at least one predetermined
soft exception.

10. The method of claim 6 further comprising:initializing at least one
parameter of a queue during said modifying; andchanging at least said
parameter of said queue during said propagating;wherein said queue
supports multiple readers and is coupled between the appropriate
operator, the third operator, and a fourth operator already present in
the global plan.

11. A computer-readable storage medium encoded with instructions to
perform the acts of receiving, modifying and propagating as recited in
claim 6.

12. A data stream management system that processes streams of data using a
plurality of continuous queries, the data stream management system
comprising:a store encoded with a plurality of tuples representing a
relation, each tuple being time stamped;a memory encoded with a query
plan currently being used in execution of the continuous queries;means,
coupled to said store, for modifying the global plan in said memory in
response receipt of a new continuous query that uses said relation, if
the global plan comprises a first operator that supplies at least one
tuple of the relation, by using a multi-reader queue to couple the first
operator to a second operator to be used to implement the new continuous
query; andmeans, coupled to said means for modifying and to said store,
for propagating a state of the relation, from the first operator to the
second operator, before propagation of a new tuple having a new time
stamp.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is related to and incorporates by reference herein
in its entirety, a commonly-owned and concurrently-filed U.S. application
Ser. No.______ entitled "DYNAMICALLY SHARING A SUBTREE OF OPERATORS IN A
DATA STREAM MANAGEMENT SYSTEM OPERATING ON EXISTING QUERIES" by Namit
Jain et al., Attorney Docket No. ORA-2006-114-01 US.

BACKGROUND

[0002]It is well known in the art to process queries over continuous
streams of data using one or more computer(s) that may be called a data
stream management system (DSMS). Such a system may also be called an
event processing system (EPS) or a continuous query (CQ) system, although
in the following description of the current patent application, the term
"data stream management system" or its abbreviation "DSMS" is used. DSMS
systems typically receive from a user a textual representation of a query
(called "continuous query") that is to be applied to a stream of data.
Data in the stream changes over time, in contrast to static data that is
typically found stored in a database. Examples of data streams are: real
time stock quotes, real time traffic monitoring on highways, and real
time packet monitoring on a computer network such as the Internet.

[0003]FIG. 1A illustrates a prior art DSMS built at the Stanford
University, in which data streams from network monitoring can be
processed, to detect intrusions and generate online performance metrics,
in response to queries (called "continuous queries") on the data streams.
Note that in such data stream management systems (DSMS), each stream can
be infinitely long and the data can keep arriving indefinitely and hence
the amount of data is too large to be persisted by a database management
system (DBMS) into a database.

[0004]As shown in FIG. 1B a prior art DSMS may include a continuous query
compiler that receives a continuous query and builds a physical plan
which consists of a tree of natively supported operators. Any number of
such physical plans (one plan per query) may be combined together, before
DSMS starts normal operation, into a global plan that is to be executed.
When the DSMS starts execution, the global plan is used by a query
execution engine (also called "runtime engine") to identify data from one
or more incoming stream(s) that matches a query and based on such
identified data the engine generates output data, in a streaming fashion.

[0005]As noted above, one such system was built at Stanford University, in
a project called the Standford Stream Data Management (STREAM) Project
which is described in an article entitled "STREAM: The Stanford Data
Stream Management System" by Arvind Arasu, Brian Babcock, Shivnath Babu,
John Cieslewicz, Mayur Datar, Keith Ito, Rajeev Motwani, Utkarsh
Srivastava, and Jennifer Widom published on the Internet in 2004. The
just-described article is incorporated by reference herein in its
entirety as background.

[0010]Continuous queries (also called "persistent" queries) are typically
registered in a data stream management system (DSMS) prior to its
operation on data streams. The continuous queries are typically expressed
in a declarative language that can be parsed by the DSMS. One such
language called "continuous query language" or CQL has been developed at
Stanford University primarily based on the database query language SQL,
by adding support for real-time features, e.g. adding data stream S as a
new data type based on a series of (possibly infinite) time-stamped
tuples. Each tuple s belongs to a common schema for entire data stream S
and the time t is a monotonically non-decreasing sequence. Note that such
a data stream can contain 0, 1 or more pairs each having the same (i.e.
common) time stamp.

[0011]Stanford's CQL supports windows on streams (derived from SQL-99)
based on another new data type called "relation", defined as follows. A
relation R is an unordered group of tuples at any time instant t which is
denoted as R(t). The CQL relation differs from a relation of a standard
relational database accessed using SQL, because traditional SQL's
relation is simply a set (or bag) of tuples with no notion of time,
whereas the CQL relation (or simply "relation") is a time-varying group
of tuples (e.g. the current number of vehicles in a given stretch of a
particular highway). All stream-to-relation operators in Stanford's CQL
are based on the concept of a sliding window over a stream: a window that
at any point of time contains a historical snapshot of a finite portion
of the stream. Syntactically, sliding window operators are specified in
CQL using a window specification language, based on SQL-99.

[0012]For more information on Stanford University's CQL, see a paper by A.
Arasu, S. Babu, and J. Widom entitled "The CQL Continuous Query Language:
Semantic Foundation and Query Execution", published as Technical Report
2003-67 by Stanford University, 2003 (also published in VLDB Journal,
Volume 15, Issue 2, June 2006, at Pages 121-142). See also, another paper
by A. Arasu, S. Babu, J. Widom, entitled "An Abstract Semantics and
Concrete Language for Continuous Queries over Streams and Relations" in
9th Intl Workshop on Database programming languages, pages 1-11,
September 2003. The two papers described in this paragraph are
incorporated by reference herein in their entirety as background.

[0013]An example to illustrate continuous queries is shown in FIGS. 1C-1E.
Specifically, FIG. 1E illustrates a merged STREAM query plan for two
continuous queries, Q1 and Q2 over input streams S1 and S2. Query Q1 of
FIG. 1E is shown in detail in FIG. 1C expressed in CQL as a
windowed-aggregate query: it maintains the maximum value of S1:A for each
distinct value of S1:B over a 50,000-tuple sliding window on stream S1.
Query Q2 shown in FIG. 1D is expressed in CQL and used to stream the
result of a sliding-window join over streams S1 and S2. The window on S1
is a tuple-based window containing the last 40,000 tuples, while the
window on S2 is a 10-minutes time-based window.

[0014]Several DSMS of prior art, such as Stanford University's DSMS treat
queries as fixed entities and treat event data as an unbounded collection
of data elements. This approach has delivered results as they are
computed in near real time. However, in most continuous query systems
this prior art approach does not allow continuous queries to be added
dynamically. One reason is that a query plan is computed at the time of
registration of all queries, before such a prior art DSMS even begins
operations on streams of event data.

[0015]Once queries have registered and such a prior art DSMS begins to
process event data, the query plan cannot be changed, in prior art
systems known to the current inventors. The current inventors recognize
that adding queries can be done, for example by quiescing Stanford
University's DSMS, adding the required queries and starting up the system
again. However, the current inventors note that it gives rise to
indeterminate scenarios e.g. if a DSMS is being quiesced, there is no
defined checkpoint for data in a window for incomplete calls or for data
of intermediate computation that has already been performed at the time
the DSMS is quiesced.

[0016]In one prior art DSMS, even after it begins normal operation by
executing a continuous query Q1, it is possible for a human (e.g. network
operator) to register an "ad-hoc continuous query" Q2, for example to
check on congestion in a network. Such a query Q2 may be written to find
a fraction of traffic on a backbone link that is coming from a customer
network. In highly-dynamic environments, a data stream management system
(DSMS) is likely to see a constantly changing collection of queries and
needs to react quickly to query changes without adversely affecting the
processing of incoming time-stamped tuples (e.g. streams).

SUMMARY

[0017]A computer is programmed in accordance with the invention to
implement a data stream management system (DSMS) that receives a new
continuous query (also called simply "new query") during execution of one
or more continuous queries that have been previously registered (also
called "existing queries"). The new query is to be executed by the DSMS
on a stream or a relation, which may or may not be executed upon by
existing queries. The new query is received (e.g. from a user) during
normal operation of the DSMS in an ad-hoc manner, in the midst of
processing incoming streams of data by executing a number of existing
queries based on a global plan.

[0018]Specifically, a computer is programmed in several embodiments of the
invention to automatically modify the global plan on the fly, to
accommodate both execution of the new query and also continuing execution
of existing queries. A modified plan which results therefrom may include
new operators and/or sharing of one or more operators that are currently
being used in execution of existing queries. Accordingly, a computer in
several embodiments of the invention compiles a new query, if possible by
sharing one or more operators between the new query and one or more
existing queries.

[0019]In such embodiments, when compilation of the new query is complete,
any operators that were not previously scheduled for execution (i.e.
newly coupled operators) are also scheduled for execution, thereby to
alter the above-described processing to henceforth be based on the
modified plan. In some embodiments, any operators that were previously
scheduled continue to execute as per schedule, independent of addition of
the new query. Depending on the embodiment, execution of existing queries
is performed without any interruption, or with minimal interruption from
coupling and scheduling of execution of new operators required to execute
the new query.

[0020]Unlike Stanford University's DSMS described in the Background
section above, a new query that is added in accordance with the invention
is not pre-defined. Furthermore, unlike Stanford University's DSMS, a new
query is received and executed without a DSMS of several embodiments of
the invention being quiesced, i.e. while continuing to receive input
streams and transmit output streams. Moreover, in many embodiments, the
existing operators may transmit the current value of a relation to the
newly added operator (for the new query) via the newly created queues.
The new query of several embodiments shares execution structures as much
as possible with the existing global plan, and a newly added operator's
structure(s) are populated based on existing inputs.

[0021]Moreover, unlike the prior DSMSs of the type described in the
Background section above, a DSMS in accordance with the invention
supports addition of queries over relations in addition to streams. In
several embodiments, there is no restriction on the type of the query
being added. In some embodiments, the mechanism is also independent of
the internal representation of the relation in the server although in
certain embodiments an incremental representation of the relation is
used. In embodiments where the absolute representation of the relation is
used, the propagation mechanism as described herein continues to work
without any changes.

[0022]None of the prior art known to the inventors of the current patent
application discloses or suggests propagation of a current state of a
relation to one or more operators which are to be used by a new query.
Specifically, during operation of a DSMS in accordance with the
invention, when an operator on a relation (called "relation operator") is
awakened, the relation operator first propagates a current state of the
relation to any operator(s) that have been newly coupled thereto, for use
in execution of the new query.

[0023]In some embodiments, the current state is propagated only to those
operators that are newly coupled to an existing relation operator. The
propagation is performed so that these newly coupled operators receive
the current state information. The current state is not propagated to any
operators that were already in existence (also called "existing
operators"). After propagation of the current state, any new information
received by the relation operator is processed and results therefrom are
supplied to all operators coupled to the relation operator, including
newly-coupled operators and any existing operators. In this manner, these
embodiments continue to process input data streams, now using the
modified plan.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIGS. 1A and 1B illustrate, in a high level diagram and an
intermediate level diagram respectively, a data stream management system
of the prior art.

[0025]FIGS. 1C and 1D illustrate two queries expressed in a continuous
query language (CQL) of the prior art.

[0026]FIG. 1E illustrates a query plan of the prior art for the two
continuous queries of FIGS. 1C and 1D.

[0027]FIG. 2 illustrates, in an intermediate level diagram, a data stream
management system (DSMS) that has been extended in accordance with the
invention to support adding new continuous queries during operation on
existing continuous queries.

[0028]FIG. 3 illustrates, in a flow chart, methods that are executed by
the extended DSMS of FIG. 2, in some embodiments of the invention to
obtain a modified plan by addition of new continuous queries, and
propagation of all tuples of relation operator(s) shared with the new
continuous queries during execution of the modified plan.

[0029]FIGS. 4A-4F illustrate examples of trees of operators at different
instants of time during modification of an execution plan to add a new
continuous query, in accordance with the invention.

[0030]FIGS. 5A-5C together illustrate, in a flow chart, acts of a method
that is performed in some embodiments of the invention, to compute a
logical plan, a physical plan and modification of a global execution
plan, to add a continuous query

[0031]FIG. 6 illustrates, in a high level block diagram, hardware included
in a computer that may be used to perform the methods of FIGS. 5A-5C in
some embodiments of the invention.

DETAILED DESCRIPTION

[0032]Many embodiments of the invention use a DSMS whose continuous query
language (CQL) natively supports certain standard SQL keywords, such as a
SELECT command having a FROM clause and in addition also supports
windowing functions required for stream and/or relation operations. Note
that even though several keywords and/or syntax may be used identically
in both SQL and CQL, the semantics are different for these two languages
because SQL may be used to define queries on stored data in a database
whereas CQL is used to define queries on transient data in a data stream.

[0033]A DSMS which includes a computer programmed as described in
published literature about the Standford Stream Data Management (STREAM)
Project is extended by programming it with certain software in several
embodiments of the invention called a continuous query compiler, as
discussed below. A continuous query compiler is implemented in accordance
with the invention to receive and act on a new continuous query q in an
ad-hoc manner, e.g. on the fly during normal operation of the DSMS on
existing queries. Accordingly, such a DSMS in accordance with the
invention is hereinafter referred to as an extended DSMS.

[0034]After receipt, new continuous query q is automatically compiled by
continuous query compiler 210 (FIG. 2) performing several acts that are
normally performed to implement query compilation, and after compilation
the new continuous query q is automatically executed. Query receipt,
compilation and execution are performed by some embodiments of extended
DSMS 200 (FIG. 2) while processing incoming streams of data 250 by
executing thereon one or more continuous queries that were already being
executed ("existing queries") prior to receipt of the new continuous
query q.

[0035]For example, simultaneous with generation of output data stream 231
by execution of existing queries, continuous query compiler 210 parses
new continuous query q to build an abstract syntax tree (AST), followed
by building a tree of operators. Such a tree of operators typically
includes, one or more operators (also called "source operators") that act
as source(s) of tuples based on incoming data stream(s) 250 (FIG. 2),
and/or source(s) of a stream of information on a relation received via
link 243.

[0036]In addition to source operators (which are typically but not
necessarily located at leaf nodes), the tree of operators includes one or
more operators at intermediate nodes (called "query processing
operators") that receive data streams from the source operators, and a
single root node which includes an output operator to output the results
of processing the query. The tree of operators is typically included in a
logical plan which does not reference any physical structures. In
creating the logical plan, any semantic errors are flagged (e.g. any type
mismatches and/or references to non-existent sources of data streams).
The nodes of a tree in the logical plan are typically logical operators
that are supported by the continuous query language (CQL), such as SELECT
and JOIN.

[0037]Several embodiments then create for that same new query q various
physical operators and related resources, such as memory for a queue,
needed to execute the query. Physical operators accept data of streams
and/or relations as input and generate as output data of streams and/or
relations. In this process, if the new continuous query q uses an
operator already existing in a global plan located in memory 290 that is
currently being executed (also called "executing plan") by query
execution engine 230 on incoming stream(s) 250, then continuous query
compiler 210 does not create a new physical operator. Instead, continuous
query compiler 210 just modifies the executing plan in memory 290.

[0038]An executing plan which is currently being used by DSMS 200 contains
physical resources of all operators for all queries currently being
executed. When a new query is received for execution in act 301, then as
per act 308 in FIG. 3, to support execution of the new query, continuous
query compiler 210 updates the global plan, e.g. by reusing existing
components (such as operators, stores and queues) and creates new
components as necessary. For example, compiler 210 creates one or more
new outputs for one or more operators existing in a global plan that is
currently being executed by DSMS 200, and also creates one or more new
operators (e.g. to generate an output stream to be included in stream
231) for the new query.

[0039]Then, as per act 309, continuous query compiler 210 alters the
processing of incoming data streams 250 by query execution engine 230.
After being altered, query execution engine 230 continues its processing
of incoming data streams 250 by executing thereon not only the existing
queries but also the new query. In some embodiments, a scheduler is
invoked to allocate time slot(s) for any new operator(s) of the new query
that are referenced in the modified plan that results from modification
in act 308. Execution of the modified plan eventually results in
execution of the new continuous query at an appropriate time (depending
on when its operators are scheduled for execution), in addition to
execution of existing queries. Some embodiments of the invention use a
lock (e.g. a reentrant read write lock), to serialize updating of an
operator by compiler 210 and its execution.

[0040]In some embodiments, any output(s) that is/are newly added to a
relation operator is/are identified in the modified plan as such (e.g.
flagged as requiring initialization), to support propagation thereto of
the relation's current state, either before or at least when the relation
operator is next awakened. After state propagation, the relation operator
continues may process an incoming stream of data about a relation.
Specifically, the processing continues wherever the relation operator had
left off, when a prior time slot ended. As noted above, a scheduler
allocates time slots in which the relation operator executes. On being
awakened, the relation operator of some embodiments first propagates any
new information on the relation that is received by the relation
operator. Results of processing the new information is/are thereafter
made available for reading at all outputs of the relation operator
(including the newly added output).

[0041]Act 301 and portions of 308 (e.g. query parsing and logical tree
construction) may be performed by continuous query compiler 210 of
extended DSMS 200 in a manner similar or identical to a normal DSMS,
unless described otherwise herein. Extended DSMS 200 of some embodiments
accounts for the fact that new continuous queries can be added at any
time during operation of extended DSMS 200 (e.g. while executing
previously registered continuous queries), by any operator A checking
(e.g. on being awakened in act 310) if the output of the operator A is a
stream (as per act 311 in FIG. 3). If not a stream, the operator A
further checks whether any new outputs resulting from compiling the new
query Q1 (received in act 301) have been added for each relation (as per
act 312 in FIG. 3) and if so propagating that relation's current state
(obtained via line 244 in FIG. 2) to the new outputs (as per act 313 in
FIG. 3). In the embodiment illustrated in FIG. 3, if the result in act
311 is yes (i.e. the operator's output is a stream), then control
transfers directly to act 314. Note that other embodiments of DSMS 200
may implement the propagation of a relation's state prior to altering the
processing by engine 230, i.e. independent of each operator's awakening
and execution.

[0042]Also, awakening of operators in an executing plan and propagation of
a relation's state can be performed in any order relative to one another
depending on the embodiment. For example, although act 310 (to awaken an
operator) is shown as being performed before act 313 in FIG. 3, other
embodiments perform act 313 before performing act 310. Operator awakening
in some embodiments is performed by a scheduler in query execution engine
230 that is programmed to automatically determine (e.g. in a round robin
fashion) an order of execution of each operator relative to other
operators. The scheduler's list of operators is updated with any new
operators that may be required for new queries during registration.
Depending on the embodiment, the scheduler may either preallocate time
slots to all operators, or alternatively allocate time slots to each
operator individually in a dynamic just-in-time manner.

[0043]Accordingly, during registration of each new continuous query, the
scheduler allocates a time slice for execution of each new operator
therein. In several embodiments, the scheduler operates without
interrupting one or more operators that are being executed in a current
time slice. Hence, in some embodiments, the processing of existing
queries is altered to permit processing of the new query thereby to
effect a switchover from a currently executing plan to a modified
executing plan. In an illustrative embodiment, altering of normal
processing is performed at the end of a current time slice, with no delay
(i.e. not noticeable in output stream 231 in FIG. 2) in execution of
existing queries.

[0044]Accordingly, after registration of a new continuous query as
described above, the extended DSMS continues to perform processing of
input data streams 250 in the normal manner but now using the new query
in addition to existing queries, i.e. based on the modified plan. Hence,
output data streams 231 that were being generated by execution of
existing queries continue to be generated without interruption, but are
supplemented after the altering of processing, by one or more data
streams from an output operator of the new continuous query, i.e. by
execution of the new continuous query.

[0045]Depending on the embodiment, an unmodified plan (i.e. a global plan
prior to modification) may be originally created, prior to receipt of the
new continuous query, by merging of several physical plans for
corresponding queries that are currently being executed. The specific
methods being used in merging can be different, depending on the
embodiment. In some embodiments, a new physical plan is merged into an
unmodified plan by sharing just event source operators therebetween, as
discussed below in reference to FIGS. 5A-5C. Several other embodiments
perform on-the-fly merging of a physical plan for a new query, with a
plan that is currently being executed for existing queries, by sharing
not only source operators but also operators at intermediate nodes of an
operator tree for the new query, as described in for example, US Patent
Application [ATTORNEY DOCKET OID-2006-114-01] which is incorporated by
reference, as noted at the beginning of the current patent application.

[0046]Information about a relation that is supplied by link 244 is
typically held in a store 280 in extended DSMS 200. Store 280 is
typically multi-ported in order to enable multiple readers to access
information stored therein. Store 280 may be used to store a relation R's
information such as a current state R(t). In certain embodiments relation
R is represented in an incremental manner, by tuples that are time
stamped, and represent requests for incremental changes to the relation's
initial state R(0). An example of a relation that may be represented in
this manner is the number of chairs in a conference room. However, other
embodiments do not use tuples, and instead maintain in memory an image of
the relation's current state R(t), and this image is changed dynamically
as relation R changes over time. An example of a relation that may be
represented by an image is a Range Window operator on a stream, e.g. if
window depth is 10, then such an image holds just 10 tuples.

[0047]In a conference room example for a relation operator described
above, current state is propagated based on the relation's incremental
representation. Specifically, in this example, the number of chairs in a
given conference room is one integer, which changes whenever a new chair
gets added or removed from the conference room. Instead of propagating
all the number of chairs from the beginning of time, which might be a
very large stream, we will only propagate the current value of the number
of chairs (which is just 1 integer or 1 long depending on the storage
type used for the number of chairs). So, at the point at which a new
query is added, one illustrative DSMS embodiment simply propagates the
value of the relation at that point in time, which depends on the changes
from the beginning in time, but may not contain all the changes (because
an item which got added and then removed subsequently does not count).

[0048]In embodiments that use tuples to represent a relation, tuples are
typically received in extended DSMS 200 in the form of a data stream,
e.g. carried by a communication link 242 from a user as shown in FIG. 2.
Depending on the embodiment, the tuples of a relation may represent
requests for two types of changes, namely requests to insert information
or requests to delete previously inserted information, which may
respectively constitute an Istream or Dstream.

[0049]The just-described stream representation of a relation in some
embodiments, by time stamped tuples, is also referred to herein as an
incremental representation. Although the incremental representation of a
relation uses streams (i.e. Istream and Dstream), note that the
relation's state is relatively static (e.g. relative to data stream 250).
Hence, in practice, streams Istream and Dstream for a relation are
several orders of magnitude smaller (in the rate of information flowing
therein) than streams normally processed by extended DSMS 200. Use of
Istream and Dstream to represent such a static relation enables several
embodiments to process all information in extended DSMS 200 using a
single data type, namely the stream data type. In contrast, as noted
above, certain alternative embodiments of the invention store a
relation's current state information in a non-incremental representation
and hence use both data types.

[0050]Embodiments that use an incremental representation of a relation may
implement the act of propagating the relation's state by reading the
relation's initial state and all subsequent tuples from relational store
280 as illustrated in act 313 of FIG. 3. Some embodiments use a queue to
communicate references to tuple references (e.g. pointers to tuples)
between a relational operator and any operators coupled thereto (as the
queue supports multiple readers). In such embodiments, each of the
multiple outputs of the queue initially supplies a current state of a
relation R from store 280, for propagation to the respectively coupled
readers.

[0051]Moreover, each of the multiple outputs of the queue identifies any
tuple references in the queue that have not yet been read by its
respectively coupled reader. A tuple reference remains in the queue until
readers coupled to all outputs of the queue have read the tuple
reference, at which time the tuple reference is deleted from the queue.
The tuple references are typically arranged in order of receipt relative
to one another. A newly added output of the queue may identify to its
newly-added reader one or more tuple references that have been already
read by other readers coupled to other outputs of the queue. The
just-described already-read tuple references may be added to the queue
during propagation of current state of a relation, e.g. to initialize the
newly added output.

[0052]Furthermore, in these embodiments, the current state of the relation
is maintained in store 280. Note that it is only applicable to operators
whose output is a relation. Also a data structure (e.g. a bit map) is
maintained to denote the newly coupled operators. Accordingly, execution
of a new continuous query in such embodiments begins with each relation's
current state being propagated to the newly coupled operators. In these
embodiments, execution of the new continuous query on streams (in
contrast to relations) does not use any current state (since there is
none) and instead uses new tuples that are time stamped after the current
time (at which time execution resumes).

[0053]In some embodiments, a multi-reader queue of the type described
above enables propagation (by reading) of a relation's state selectively
to only certain operators that are being used in a new continuous query
which did not previously read this information. Such selectivity avoids
propagation of past tuples multiple times, to operators of existing
queries. More specifically, the queue of certain embodiments supports
marking by each operator of tuples in a relational store as being
available to be read only by individually identified outputs of the queue
that have been newly added, for execution of the new continuous query.

[0054]The above-described queue may be implemented in any manner well
known in the art, although certain embodiments of the invention use the
following implementation. The queue does not itself contain any tuples
and instead it contains references to a store (which may be a relational
store or a window store) in which the tuples are stored. Each output (and
hence reader) of the queue has a read pointer which is advanced when a
tuple for that output is read from the store. The queue initially holds
references to all tuples that are received, until a tuple is read by all
readers of the queue, at which time that tuple's reference is
automatically deleted from the queue. For example, if a 1.sup.st
continuous query is received at time 100 and a 2.sup.nd continuous query
is received at time 300, and if a tuple of a stream used by both queries
came in at time 175 and its negative came in at time 275, then the
2.sup.nd query never sees this tuple, although references to the tuple
and its negative are both seen by the 1.sup.st query. A negative of a
tuple typically represents a request to delete information inserted by
the tuple, which is an incremental change as discussed in paragraph
[0042].

[0055]Depending on the embodiment, even when a tuple's reference is
deleted from a queue, that particular tuple itself may still exist in the
underlying store, for example for use by another queue. The store is
implemented in such embodiments with the semantics of a bag of tuples
that are written by the queue. These tuples are read by multiple readers
of a queue that have been added as subscribers to the store, and each
reader may individually dequeue a given tuple's reference, from that
reader's view of the queue, after reading the given tuple from the queue.
In such embodiments, the queue has only one writer, to write each tuple
just once into the store, on receipt of the tuple by extended DSMS 200
from an outside stream (e.g. from a user).

[0056]In several embodiments, a store is created for and owned by a
physical operator (such as a range window operator on a stream) that is
used in a continuous query (hereinafter "1.sup.st continuous query").
Hence, store is automatically shared when the same physical operator is
also used in a 2.sup.nd continuous query which is added subsequent to
start of execution of the 1.sup.st continuous query. In some embodiments,
only operators that are sources of data for the 2.sup.nd continuous query
(typically, but not necessarily, leaf node operators) are shared. In such
embodiments, the only requirement to share operators is that they have an
identical name (of a relation or stream) that is being sourced therefrom.

[0057]Depending on the embodiment, a physical operator for the 1.sup.st
continuous query may read data from a relation's store or from a store of
a window on a stream, using a queue which may be same as or different
from the queue used by the same physical operator when executed for the
2.sup.nd continuous query. A single physical operator that is used in
execution of different queries may itself use a single queue to support
multiple readers in the different queues of some embodiments, although in
other embodiments different queues are used by the same physical operator
in different queries.

[0058]For example, assume that a store (hereinafter "window store") for a
stream operator of an illustrative embodiment holds stream tuples A, B, C
and D (also called messages A, B, C and D). If tuple A has been read by
the 1.sup.st continuous query from the window store, then tuple A is
dequeued from the 1.sup.st queue but the same tuple A remains in the
window store until a later point in time when tuple A is dequeued by the
2.sup.nd queue. In this embodiment, tuple A is not deleted from the
window store until tuple A has been read by all subscribers that read
from the window store, at which time it is automatically deleted.

[0059]In the just-described example, after tuple A has been deleted from
the window store, if a 3.sup.rd queue has a new reader that now
subscribes to the window store, then the 3.sup.rd queue may once again
insert the same tuple A into the window store, but at this stage the
re-inserted tuple A is not available to the 1.sup.st queue and to the
2.sup.nd queue (both of which have already read tuple A). This is because
messages being inserted for the 3.sup.rd queue are directed only to its
reader (i.e. 3.sup.rd queue's reader), and not to the readers of the
1.sup.st queue and the 2.sup.nd queue.

[0060]Propagation to new outputs (see act 313 in FIG. 3) of a relation's
current state is performed in some embodiments in a transparent manner,
i.e. without any failure that requires a user's attention, whereby soft
errors and/or soft exceptions are automatically handled transparent to
the user. Examples of soft errors include lack of a resource, such as
memory. For example, a transparency feature may be implemented in some
embodiments by architecting propagation of a relation's state to be
responsive to soft errors (e.g. lack of memory), by automatically
suspending the propagation until the soft error is resolved, followed by
automatically resuming the propagation after the soft error is resolved.
The transparency feature which is used in some embodiments ensures that
the user is not notified of a failure to propagate, because user is not
involved in starting such propagation.

[0061]In some embodiments, only bottom-most operators in an execution tree
are shared among queries as described herein, namely operators at level
L=0, which directly receive tuples of event data in extended DSMS 200
from outside. Such operators do not have any other inputs, and hence they
can be shared between different queries as long as the operators have the
same name, e.g. if the operators represent the same relation. Alternative
embodiments of the invention check if operators at higher levels can be
shared. Specifically some alternative embodiments check if operators at
level L>0, e.g. if a Join operator used for executing existing queries
can be shared with a new continuous query. Such alternative embodiments
may check if a subtree rooted at p can be implemented by a subgraph in
the currently executing plan.

[0062]During the propagation of entire state of a relation in act 313, all
tuples with a current time stamp are propagated, including both insert
requests and delete requests, in embodiments that use these form of
tuples as described above, in paragraph [0042]. Hence, it will be
apparent to the skilled artisan, from this disclosure that the extended
DSMS 200 thereafter behaves as if the new continuous queries were always
present (relative to the relation). Such behavior enables the extended
DSMS 200 to execute the new continuous query in a manner consistent with
its execution of one or more existing continuous queries. Hence, if a new
continuous query happens to be identical to a existing continuous query,
identical streams are thereafter produced, as outputs thereof.

[0063]Next, a new tuple of the relation is propagated (as per act 314), to
all outputs of the corresponding operator (i.e. to new outputs as well as
pre-existing outputs of the relation operator). The new tuple of a
relation may be generated in any manner, depending on the embodiment. For
example, the new tuple may arise from changes to a relation that are
identified by a user, via a communication link 242 into store 280 of
extended DSMS 200 (FIG. 2). Alternatively, the new tuple may also be
generated within the extended DSMS 200 itself, e.g. by a window operator
in query execution engine 230 from a stream, which new tuple is stored
via line 241 (FIG. 2) in store 280. Note that act 313 (FIG. 3) is not
required in case of execution of a stream operator by query execution
engine 230, which transfers control via branch 316 directly to act 314.
Act 314, as noted above, propagates the new tuple to all outputs of the
operator (in this case, the stream operator).

[0064]Depending on the embodiment, the extended DSMS 200 may perform act
313 at any time before act 314, after execution resumes with the modified
executing plan. In some embodiments, act 313 is performed at whatever
time the relation operator that is being shared (between one or more
existing queries and one or more new continuous queries) is scheduled to
be executed next. In several embodiments, extended DSMS 200 schedules
operators on a round-robin basis, although other scheduling mechanisms
may also be used in accordance with the invention, depending on the
embodiment.

[0065]In certain alternative embodiments, act 313 (FIG. 3) may be
performed even before the scheduled awakening of, and execution of the
shared relation operator, depending on the architecture (e.g. if a
relation operator is architected to propagate only incremental changes to
state and does not contain functionality to propagate the entire state of
the relation). As noted elsewhere herein, in some embodiments the
relation does not have an incremental representation at all and instead a
complete value of the relation is propagated every time, in which case
propagation by act 313 is not performed.

[0066]Note that although a procedure for propagating previously-received
information to an operator's newly added outputs has been described above
in the context of sourcing tuples of a relation, the same procedure may
also be used in some embodiments by an operator that sources tuples of a
view relation operator (i.e. an operator that sources the information to
implement a view on top of a relation). In this context, a view of
extended DSMS 200 has the same semantics as a view in a prior art
database management system (DMS).

[0067]Operation of extended DSMS 200 of some embodiments is further
described now, in the context of an illustrative example shown in FIGS.
4A-4E. Specifically, FIG. 4A shows a tree for a query Q1 that is
registered for execution in the extended DSMS 200 at time 100, e.g. by
the user typing in the following text in a command line interpreter:

Q1: Select*from R where A>10

Assume that relation R represents the number of chairs in a conference
room. For example, if there are 25 chairs in a given conference room
(identified as ROOM-1), then its identity (ROOM-1) is returned as the
result of the query, because this number 25 is more than 10.

[0068]On receiving the above-described continuous query, extended DSMS 200
creates a query object illustrated in FIG. 4B, and stores the root of an
optimized physical plan for the query. Note that the root of this plan is
not the output operator O1, and instead the root is the operator A>10
(FIG. 4B). Next, extended DSMS 200 starts execution of this plan to
generate a stream of output tuples, with the first tuple being O1(100) of
value ROOM-1 and at time 500 a current tuple being O1(500) of value
ROOM-2 (e.g. if some chairs were moved at this time, from ROOM-1 to
ROOM-2). In this example, the identity of the conference room changes, at
time 500. More specifically, at time 500, the state of relation R is
changed by a delete request for ROOM-1 and an insert request for ROOM-2.

[0069]Also at time 500.5, assume a new query Q2 is registered for
execution in the extended DSMS 200, e.g. by the user typing in the
following text in a command line interpreter:

Q2: Select*from R where A>20

In this example, as seen from FIG. 4C, a tree for query Q2 is almost
identical to the corresponding tree for query Q1 shown in FIG. 4A. The
only difference between these two queries is the filter, i.e. A>20 is
used by Q2 whereas A>10 is used by Q1. Hence, a tree 220 (FIG. 2) for
query Q2 is initially generated by the continuous query compiler 210, and
a structure of this tree is illustrated in FIG. 4C.

[0070]Accordingly, relation operator R can be shared, in a modified plan
for execution of both queries Q1 and Q2 as illustrated in FIG. 4D. Hence,
as noted above, a continuous query compiler 210 generates the modified
plan by modifying existing plan in memory 290 (FIG. 2), and when this is
done a query execution engine 230 propagates the current relation state
(i.e. all tuples with the current time stamp) to filter A>20, as per
act 313 (FIG. 3). As noted above, the state of relation R changed at time
500 (before the new query got registered), and hence the latest value of
the relation, which is insert request for ROOM-2 is propagated to the
filter A>20. The insert request for ROOM-2 is thereafter supplied in
an output O2(501) as per FIG. 4E, because the corresponding value of A,
i.e. the number 25 is more than 20. Note that the insert and delete
requests were already previously propagated to filter A>10, and for
this reason are not again propagated at this time.

[0071]Subsequently, the relation operator R supplies any new tuple at time
501 (see FIG. 4E) to both its outputs and therefore that new tuple is
supplied to both filters A>10 and A>20, which in turn generate
their corresponding outputs O1(501) and O2(501) for transfer to their
respective destinations (not shown in FIG. 4E). After execution of query
Q2 has begun, and after outputs O1(501) and O2(501) have been generated
as just described (FIG. 4E), in a similar manner at a future time, a new
query Q3 may be submitted to extended DSMS 200, by a user. As shown in
FIG. 4F, an example of such a query Q3 may filter the outputs of queries
Q1 and Q2 using the respective operators O3 and O4, followed by joining
of the filtered results via operator O5. Hence, in this example, the
output operators O1 and O2 of queries Q1 and Q2 are modified in some
embodiments by adding new queues which from the inputs to new operators
O3 and O4, which in turn supply their output streams as input streams to
another new operator O5.

[0072]In some embodiments, a computer of extended DSMS 200 is programmed
to perform the three methods illustrated in FIGS. 5A-5C, to sequentially
compute each of a logical plan, a physical plan and to modify an
executing plan, as discussed next. Specifically, a query is received in
act 301 (FIG. 5A), followed by parsing of the query and performance of
semantic analysis in act 301A, followed by building of a syntax tree in
act 302A, followed by building of a tree of logical operators in act
302B. Note that the just-described acts can be performed in any manner
known in the prior art, e.g. as in any prior art DSMS.

[0073]FIG. 5A illustrates how a new logical plan for the query is created,
a new physical plan is created and merged with the global plan. So, at
the end, DSMS of some embodiments contain a global physical plan (for all
the queries registered in the server so far) and a logical plan for the
query newly registered. Note that the logical plan is not used from now
on in such DSMS. FIG. 5B illustrates how the global physical plan is
instantiated. Specifically, the whole plan is traversed again, and the
newly created physical operators (the ones that have been newly created
as a result of compilation of the newly added query in FIG. 5A) are
partially instantiated. During instantiation time, the DSMS of certain
embodiments determines what kind of stores and queues will be needed for
linking the newly created physical operators. Finally, note that FIG. 5C
shows how the global plan is traversed again, and the newly created
physical operators (the one that have been newly created as a result of
compilation of the newly added query in FIG. 5A) are completely
instantiated. Using the information obtained during the steps at FIG. 5B,
the appropriate execution structures are created. So, the DSMS of several
embodiments determines whether to create a new store or not, and if yes,
what type of store to create in FIG. 5B, but actually creates the
execution store itself in the steps shown in FIG. 5C.

[0074]In act 501, the level L is set to zero, after which time the
computer enters a loop between act 502 (which initializes a current
operator Oi to a source operator at level L) and act 507 (which
increments the level unless root is reached in which case control
transfers to act 508, indicative that the first pass has been completed).
In the just-described loop of FIG. 5A, extended DSMS 200 is programmed in
several embodiments to traverse the tree of logical operators (built in
act 302B), in a bottom-up manner as discussed next although other
embodiments of the invention may traverse such a tree in a different
order.

[0075]After act 502 (FIG. 5A), the computer checks if there exists a
source operator in a global plan that is currently being executed, for
the source operator Oi selected in act 502. Note that in this act, the
illustrative embodiment checks only on source operators, such as a source
of a relation or a source of a stream. If the answer is no, then as per
act 504, the computer creates a new physical operator in a global plan
(which is global across multiple queries), and thereafter proceeds to act
505. In the illustrative embodiment, if the operator is not a source
operator, then also act 504 is performed, i.e. a new physical operator is
created if the corresponding logical operator (such as a filter) is not a
source (of a stream or relation).

[0076]Next, in act 505, the computer saves a pointer to the physical
operator that was created in act 504 or alternatively found to exist in
act 503. After saving the pointer, the computer goes to act 506 to
increment operator Oi to the next operator in current level L and
transfer control to act 503, unless there are no more unvisited operators
in level L in which case control transfers to act 507 (discussed in the
previous paragraph), after which the first pass is completed.

[0077]Next, a second pass is begun by the computer as illustrated in FIG.
5B for some embodiments. Specifically, in such embodiments, the computer
performs act 511 (FIG. 5B) wherein the level L is set to zero, after
which time the computer enters a loop between act 512 of FIG. 5B (which
initializes a current operator Oi to a first operator at level L) and act
517 of FIG. 5B (which increments the level unless root is reached in
which case control transfers to act 518 (FIG. 5B), indicative that the
second pass has been completed, and the physical plan computed).

[0078]Referring to FIG. 5B, after act 512 the computer checks (in act 513)
if an operator has been instantiated, for the logical operator Oi
selected in act 512. If the answer is no, then the computer instantiates
the operator as per operation 520 described in the next paragraph below,
and thereafter proceeds to act 516 (FIG. 5B). In act 513 if the answer is
yes, the computer directly goes to act 516. In act 516, the computer
increments operator Oi to the next operator in current level L and
transfers control to act 513, unless there are no more unvisited
operators in level L in which case control transfers to act 517 (FIG.
5B), after which the second pass is completed. Note that several acts
511, 512, 516 and 517 in FIG. 5B are similar or identical to
corresponding acts 501, 502, 506 and 507 in FIG. 5A.

[0079]During operation 520 to instantiate an operator, the computer of
some embodiments may be programmed to perform a number of acts 521-526 as
discussed next, although in other embodiments this operation 520 may be
performed by other acts that will be apparent to the skilled artisan in
view of this disclosure. Specifically, in act 521, the computer creates
an output queue, unless this operator Oi is an output operator. Next, in
act 522 the computer adds operator Oi as reader of output queues, of
operators that supply input to operator Oi. In act 522, memory is
allocated in some embodiments, to hold one or more pointers that are used
to implement the reader. Thereafter, in act 523, the computer checks if
operator Oi's inputs result evaluates to a stream. If result in act 524
is not a stream, then the computer gets the input operator Oi and invokes
a function to take note (by setting a flag, also called
propagation-needed flag) of the need to propagate the current state
thereof, as per act 524, followed by transfer of control to act 525. If
the result in act 523 is a stream, then act 524 is skipped and the
computer directly transfers control to act 525. In some embodiments,
whenever the execution operator is next invoked by the scheduler, its
state is propagated if the just-described propagation-needed flag is set.

[0080]In act 525, the computer checks if operator Oi's input operator's
store(s) can be shared by Oi. If the store(s) cannot be shared, then the
computer allocates memory for a store to hold event data being output by
operator Oi (as per act 526), followed by transferring control to act
527. Note that control also transfers to act 527 if an answer in act 525
is yes. In act 527, the computer saves a pointer to output store in Oi,
and then adds (as per act 528) operator Oi as a reader of the output
stores of the input operators of Oi. In act 528, additional memory is
allocated in some embodiments, to hold one or more pointers that are used
to implement the reader. This completes operation 520. Thereafter, in act
517 of FIG. 5B, level L is incremented and control transfers to act 513,
unless the root is reached in which case control transfers to act 518. On
reaching act 518, the second pass is completed, and the physical plan for
the new query has been computed.

[0081]Next, a third pass is begun by the computer as illustrated in FIG.
5C for some embodiments. Specifically, in such embodiments, in act 531
the computer again sets level L to zero, after which time the computer
again enters a loop between act 532 of FIG. 5C (which initializes a
current operator Oi to a first operator at level L) and act 537 of FIG.
5C (which increments the level unless root is reached in which case
control transfers to act 539 (FIG. 5C), indicative that the third pass
has been completed, and the executing plan has been modified).

[0082]After act 532 (FIG. 5C), the computer checks (in act 533) if
execution structures have been created, for the operator Oi selected in
act 532. If the answer is no, then the computer creates the execution
structures corresponding to physical structures identified in the
physical plan, and goes to act 536 (FIG. 5C). Note that in act 531 if the
answer is yes, the computer directly goes to act 536 (FIG. 5C). Examples
of execution structures that may be created in act 532 include, for
example, stores, queues, operators and readers.

[0083]In act 536 of FIG. 5C, the computer again increments operator Oi to
the next operator in current level L and transfers control to act 531,
unless there are no more unvisited operators in level L in which case
control transfers to act 537 (FIG. 5C) as discussed above. Note that
several acts 531, 532, 536 and 537 in FIG. 5C are similar or identical to
corresponding acts in FIGS. 5A and 5B.

[0084]In act 533 (FIG. 5C), the computer continues executing queries, this
time in the modified executing plan rather than the unmodified executing
plan being used when the new query was received. Act 533 begins execution
of the newly-added query, and also begins execution of any queries that
are referenced therein, such as a view which was never used before. Such
a view in turn may reference another query, whose execution is therefore
also started, in order to support execution of the newly-added query.

[0085]Note that the extended data stream management system 200 may be
implemented in some embodiments by use of a computer (e.g. an IBM PC) or
workstation (e.g. Sun Ultra 20) that is programmed with an application
server, of the type available from Oracle Corporation of Redwood Shores,
Calif. Such a computer can be implemented by use of hardware that forms a
computer system 600 as illustrated in FIG. 6. Specifically, computer
system 600 includes a bus 602 (FIG. 6) or other communication mechanism
for communicating information, and a processor 604 coupled with bus 602
for processing information.

[0086]Computer system 600 also includes a main memory 606, such as a
random access memory (RAM) or other dynamic storage device, coupled to
bus 602 for storing information and instructions to be executed by
processor 604. Main memory 606 also may be used for storing temporary
variables or other intermediate information during execution of
instructions to be executed by processor 604. Computer system 600 further
includes a read only memory (ROM) 608 or other static storage device
coupled to bus 602 for storing static information and instructions for
processor 604. A storage device 610, such as a magnetic disk or optical
disk, is provided and coupled to bus 602 for storing information and
instructions.

[0087]Computer system 600 may be coupled via bus 602 to a display 612,
such as a cathode ray tube (CRT), for displaying to a computer user, any
information related to DSMS 200 such as a data stream 231 that is being
output by computer system 600. An example of data stream 231 is a
continuous display of stock quotes, e.g. in a horizontal stripe at the
bottom of display 612. An input device 614, including alphanumeric and
other keys, is coupled to bus 602 for communicating information and
command selections to processor 604. Another type of user input device is
cursor control 616, such as a mouse, a trackball, or cursor direction
keys for communicating direction information and command selections to
processor 604 and for controlling cursor movement on display 612. This
input device typically has two degrees of freedom in two axes, a first
axis (e.g., x) and a second axis (e.g., y), that allows the device to
specify positions in a plane.

[0088]As described elsewhere herein, incrementing of multi-session
counters, shared compilation for multiple sessions, and execution of
compiled code from shared memory are performed by computer system 600 in
response to processor 604 executing instructions programmed to perform
the above-described acts and contained in main memory 606. Such
instructions may be read into main memory 606 from another
computer-readable medium, such as storage device 610. Execution of
instructions contained in main memory 606 causes processor 604 to perform
the process steps described herein. In alternative embodiments,
hard-wired circuitry may be used in place of or in combination with
software instructions to implement an embodiment of the type illustrated
in FIGS. 5A-5C. Thus, embodiments of the invention are not limited to any
specific combination of hardware circuitry and software.

[0089]The term "computer-readable medium" as used herein refers to any
medium that participates in providing instructions to processor 604 for
execution. Such a medium may take many forms, including but not limited
to, non-volatile media, volatile media, and transmission media.
Non-volatile media includes, for example, optical or magnetic disks, such
as storage device 610. Volatile media includes dynamic memory, such as
main memory 606. Transmission media includes coaxial cables, copper wire
and fiber optics, including the wires that comprise bus 602. Transmission
media can also take the form of acoustic or light waves, such as those
generated during radio-wave and infra-red data communications.

[0090]Common forms of computer-readable media include, for example, a
floppy disk, a flexible disk, hard disk, magnetic tape, or any other
magnetic medium, a CD-ROM, any other optical medium, punch cards, paper
tape, any other physical medium with patterns of holes, a RAM, a PROM,
and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier
wave as described hereinafter, or any other medium from which a computer
can read.

[0091]Various forms of computer readable media may be involved in carrying
the above-described instructions to processor 604 to implement an
embodiment of the type illustrated in FIGS. 5A-5C. For example, such
instructions may initially be carried on a magnetic disk of a remote
computer. The remote computer can load such instructions into its dynamic
memory and send the instructions over a telephone line using a modem. A
modem local to computer system 600 can receive such instructions on the
telephone line and use an infra-red transmitter to convert the received
instructions to an infra-red signal. An infra-red detector can receive
the instructions carried in the infra-red signal and appropriate
circuitry can place the instructions on bus 602. Bus 602 carries the
instructions to main memory 606, in which processor 604 executes the
instructions contained therein. The instructions held in main memory 606
may optionally be stored on storage device 610 either before or after
execution by processor 604.

[0092]Computer system 600 also includes a communication interface 618
coupled to bus 602. Communication interface 618 provides a two-way data
communication coupling to a network link 620 that is connected to a local
network 622. Local network 622 may interconnect multiple computers (as
described above). For example, communication interface 618 may be an
integrated services digital network (ISDN) card or a modem to provide a
data communication connection to a corresponding type of telephone line.
As another example, communication interface 618 may be a local area
network (LAN) card to provide a data communication connection to a
compatible LAN. Wireless links may also be implemented. In any such
implementation, communication interface 618 sends and receives
electrical, electromagnetic or optical signals that carry digital data
streams representing various types of information.

[0093]Network link 620 typically provides data communication through one
or more networks to other data devices. For example, network link 620 may
provide a connection through local network 622 to a host computer 624 or
to data equipment operated by an Internet Service Provider (ISP) 626. ISP
626 in turn provides data communication services through the world wide
packet data communication network 628 now commonly referred to as the
"Internet". Local network 622 and network 628 both use electrical,
electromagnetic or optical signals that carry digital data streams. The
signals through the various networks and the signals on network link 620
and through communication interface 618, which carry the digital data to
and from computer system 600, are exemplary forms of carrier waves
transporting the information.

[0094]Computer system 600 can send messages and receive data, including
program code, through the network(s), network link 620 and communication
interface 618. In the Internet example, a server 530 might transmit a
code bundle through Internet 628, ISP 626, local network 622 and
communication interface 618. In accordance with the invention, one such
downloaded set of instructions implements an embodiment of the type
illustrated in FIGS. 5A-5C. The received set of instructions may be
executed by processor 604 as received, and/or stored in storage device
610, or other non-volatile storage for later execution. In this manner,
computer system 600 may obtain the instructions in the form of a carrier
wave.

[0095]Other than changes of the type described above, the data stream
management system (DSMS) of several embodiments of the current invention
operates in a manner similar or identical to Stanford University's DSMS.
Hence, the relation operator in such a computer propagates any new tuples
that have a new time stamp to all query operators coupled thereto,
including the newly coupled query operator. In this manner, a computer
that is programmed in accordance with the invention to receive and
execute new continuous queries while continuing to operate on existing
continuous queries, without prior art issues that otherwise arise from
updating relation operators during modification of an executing plan.

[0096]In some embodiments, the DSMS uses a logical plan for each query, in
addition to a global physical plan and a global execution plan for all
the queries registered in the system. In these embodiments, in the global
physical plan, the operators are linked with each other directly, whereas
in the global execution plan, they are completely independent of each
other, and are indirectly linked with each other via queues. Moreover, in
several such embodiments, a global physical plan contains physical
operators, whereas a global execution plan contain execution operators.
As noted above also, the physical operators of certain embodiments are
directly linked with each other, whereas the execution operators are not.
Physical operators of many embodiments contain the compile-time
information, whereas the execution operators contain the run-time
information and are scheduled by the scheduler. The compiler of certain
embodiments uses the physical plan for all the optimizations (merging,
sharing, the type of store to be used etc.) and then the corresponding
execution operators are created.

[0097]Numerous modifications and adaptations of the embodiments described
herein will be apparent to the skilled artisan in view of this current
disclosure. Accordingly numerous such modifications and adaptations are
encompassed by the attached claims.

[0098]Following Subsections A and B are integral portions of the current
patent application and are incorporated by reference herein in their
entirety. Subsection A describes one illustrative embodiment in
accordance with the invention. Subsection B describes pseudo-code that is
implemented by the embodiment illustrated in Subsection A.

SUBSECTION A (of Detailed Description)

[0099]A method performed in some embodiments is illustrated in the
following pseudo-code.

TABLE-US-00001
1. Registering a query Q with the system
a. This is done as per act 301 in FIG. 5A. An object for the query is
created in
metadata. In some embodiments, a command interpreter receives the user's
text for the
query.
b. At this point, the query text is parsed, semantic analysis is done
(and if there are no
user errors in the query specification) the logical plan is computed, the
physical plan is
computed and the physical plan is also optimized. This is done as
illustrated by acts
301A-518 (spanning FIGS. 5A and 5B)
c. After completion of semantic analysis, the list of from clause
entities are visited to
determine if this query has any direct dependencies on views. For each of
the views that
this query directly depends on, the query associated with the view is
obtained and is
stored in the Query object as the set of query dependencies; This is done
as part of act
301A in FIG. 5A.
d. A Query object is created and it stores the root of the optimized
physical plan for
the query. Note that the root of this plan is not the Output operator.
e. As part of the physical plan computation, sharing of the common (with
other
queries) base tables and views is also achieved. View sharing involves
"pointing" to the
view root operator that is "above" the root operator for the query
associated with the
view. For base table and view, sources that are referenced for the first
time by this query
(i.e. no other registered query in the system references these base
tables/views), a
Stream Source operator and a View Root operator are created and stored in
a global array of source operators maintained in the DSMS. This is
illustrated in act 504.
2. Destinations for the query Q are specified.
a. A physical layer Output operator is created. This results in the
creation of the Output operator and its association with the Input/Output
driver corresponding to the specified destination. The instance of the
Output operator created is returned. See act 504
b. The returned Output operator is added to a list of outputs for
the query and stored inside the Query object. See act 505
c. At this point, the query Q is checked if it has already been
started
d. If no (as in this case), then nothing else needs to be done
3. The query Q is started for execution
a. If the query has already been started, then do nothing and
return
b. Else, recursively, execution operators are created recursively
for the operators - see FIG. 5C.
c. The state of the query is set to STARTED, so that it doesn't get
started again. Note that this state is checked in 2 (c) above.

SUBSECTION B (of Detailed Description)

[0100]A method performed in some embodiments is illustrated in the
following pseudo-code.

TABLE-US-00002
In one implementation, the internal representation of a relation is an
incremental
representation. When a new query Q is being admitted into an already
running system
(dynamic query addition), the following scenario may be encountered. There
could be a
newly created execution operator p (newly created and private to the
current query Q)
one of whose inputs is an operator c that is being shared and is already
part of the running
system when query Q is being admitted into the system.
If operator c evaluates to a relation, then the operator c first
propagates its current relation
state to the newly created operator p (which is coupled to an output of c)
(via the queue
connecting operators c and p), before sending any further data on the
relation. This is
because an incremental representation is used for relations and this
implies that a starting
snapshot (i.e. an initial state) is required on top of which subsequent
incremental data
have to be applied, to determine the state of a relation at any point in
time (the state of the
relation input from c, for the operator p).
Thus, to support dynamic query addition, several embodiments identify
existing operators
that need to propagate their relation's state, and also identify the newly
created operators
to which they should be propagating that state. Some embodiments identify
existing
operators that need to propagate their relation's current state, and also
identify for each
such existing operator the queue reader identities ("ids") corresponding
to the newly
created operators to which state is to be propagated.
Following describes a general approach used in various embodiments on top
of any
operator sharing algorithm (OSA for short) which has the following
property called
"OSA Subgraph Property": If OSA determines that an operator corresponding
to p can
be shared from the existing global execution plan, then OSA determines
that the subtree
rooted at p can be implemented by a subgraph of the existing global
execution plan.
Introduction
1. Q denotes the current query being started
2. GQ denotes the global execution plan that also implements the query Q.
GQ
forms a directed acyclic graph.
3. Plan GQ is constructed with sharing being determined using an operator
sharing
algorithm OSA that satisfies the OSA Subgraph property.
4. For each operator p in GQ there is an array of query ids called
qidarray. For each
qid in this array, operator p participates in the implementation of
the query
identified by qid.
5. The above-described array is created and maintained as part of
creation of GQ by
extending OSA.
6. The approach described below is done during the instantiation phase
for the query
Q
The Method
1. Perform the current instantiation traversal. This is a bottom-up
traversal such that
when visiting node `n`, all of its inputs have already been visited. See
operation 520
illustrated in FIG. 5B.
1.1. A current node in the traversal is denoted by n (a physical
operator).
1.2. If n is a node private to query Q (i.e. the qidarray in n, has only
one entry --the
qid for the query Q) then
1.2.1. Let inps be the array of inputs for the node n
1.2.2. for i=0; i<inps.length; i++
1.2.2.1. if inps[i] is shared in GQ (qidarray.length > 1) and
inps[i] is a
relation then
1.2.2.1.1. Let the queue reader id corresponding to the source
destination
pair (inps[i], n) be rid See act 522 in FIG. 5B.
1.2.2.1.2. Get an execution operator corresponding to inps[i] and
invoke
inps[i].instOp.propagateOldData(rid). See act 524 in FIG. 5B.
1.2.2.2. if inps[i] is private to Q or inps[i] evaluates to a stream,
then do
nothing; See act 523 in FIG. 5B.
1.3. If n is a shared node in GQ, then do nothing; see act 512 in FIG.
5B.
2. At the end of this traversal, the requirement would have been addressed
NOTE - in the above pseudo-code, a function propagateOldData is called
which is
implemented as follows in some embodiments:
Get the list of newly created queue readers `l`
Initialize the synopsis for the current state.
While (next tuple is present in the synopsis)
Get next tuple `t`
Enqueue `t` to `l`
End